What operand size override prefix does in 64-bits code segment instructions? and what default operand size mean? We can specify different operand sizes, 8, 16, 32 and 64 by opcode, so what operand size override prefix does(66H)?


Posted on 2010-06-07 22:34:06 by logicman112

What operand size override prefix does in 64-bits code segment instructions? and what default operand size mean? We can specify different operand sizes, 8, 16, 32 and 64 by opcode, so what operand size override prefix does(66H)?


Without opsize prefix you can't encode 16-bit-operand instructions in 64-bit mode (mov sreg, r/m16 doesn't require opsize prefix, though).
Posted on 2010-06-08 00:43:36 by baldr